The ultrasonic device shown and described in U.S. patent application Ser. No. 363,644, filed Mar. 30, 1982, now abandoned, in general, proved excellent for determining certain distances. In that invention, an electrostatically generated ultrasonic signal is directed from a preselected point toward a target and also to a calibration bar located closer to the preselected point then the target and at a known distance from it.
Reflection signals are received back from the target and calibration bar, the time delay between reception of the signals, due to the different distances involved, is determined and converted into the corresponding target distance. Preferably the transducer is actuated by single-pulse, electronic square wave.
In processing the reflected signals, that invention sets a noise level less than the amplitude of the reflected signals and large enough to cover unwanted responses, and compared the signals with the set noise level, passing only signals exceeding that noise level.
However, when that invention was installed on tomato harvesters and operated in the field certain problems developed. One of these problems appears to be related to the dust abounding in the fields; this sometimes became severe, preventing the device from consistently doing its job accurately.
Another problem was that the device did not seem to be sufficiently sheltered, not only from the dust that was stirred up by the machine on which it was mounted, but also from things that might drop down from above.
Another problem, which may or may not be related to the others, was that a great deal of noise and blurring occurred in the received or reflected signals, so that it became difficult for the responding circuits to respond accurately.
All these problems are solved, or at least mollified, by the present invention.
Objects of this invention are: to obtain improvement in the operation of the basic device, to provide for better sheltering of the transducer, to provide an improved calibration bar for the device that provides better response characteristics, and to provide a system that eliminates most if not all of the noise that was obscuring the signals obtained in the prior invention. In addition, an object of the present invention is to warn the operator when the efficiency of operation of the device has decreased whether because of accummulated dirt or for other reasons, so that fewer signals are actually being received than is tolerable under the circumstances.